An apparatus of the foregoing type typically has a hollow drive spindle which is supported in a spindle housing and has at its lower end which faces the conical shank a receiving cone for the shank. A draw rod is rotatably supported in the spindle and is movable axially between positions defined by a lower and an upper stop, which draw rod has at its lower end which faces the shank threads which can be screwed into threads provided in the shank and is connected at its upper end to a drive motor rotor so as to be fixed against rotation but axially movable relative thereto. A spring arrangement is arranged in a recess of the spindle and acts to effect chucking through the draw rod, which spring arrangement supports the lower stop.
In the case of such a conventional apparatus, for example German Auslegeschrift No. 2 045 604, (corresponds to U.S. Pat. No. 3,757,637), the shank of the tool or of an additional aggregate, for example an angle milling head or an adapter, is introduced into a receiving cone through a relative movement between the spindle housing, which in the known apparatus is a spindle carriage, and the shank. Driven by the drive motor, the thread of the draw rod screws into the thread of the shank, whereby after part of this screwing-in movement the draw rod will rest with a collar on the lower stop and, upon further rotation of the draw rod, the angle milling head is lifted up until it approximately rests on the spindle carriage which forms the spindle housing. The angle milling head can then be chucked on the spindle carriage by means of fastening screws or hydraulically operated clamping bolts. The chucking of a heavy tool occurs in a similar manner, but the conical tool shank is fully pulled into the receiving cone until it rests fixedly on same and the drive motor is automatically switched off. Due to manufacturing imprecisions, a conical shank which is constructed as a steep-angle taper can become jammed in the receiving cone. If this is the case, the draw rod unscrews through a reversed direction of rotation of its drive motor from the thread of the shank until a further movement of the draw rod is limited by the upper stop. The draw rod now presses the jammed shank out of the receiving cone. The tool or the angle milling head is released suddenly and falls downwardly due to its own weight until the draw rod rests on the lower stop. Since only a few threads are still in engagement and the thread is constructed according to the DIN-norm as a V-thread, these few threads are highly stressed and are thus exposed to rapid wear. It can even happen that the threads break off. Therefore, the threads must be examined regularly with respect to such wear. In the lowered position of the draw rod, same also serves to swing the angle milling head which hangs on it into a different angular position through rotation of the draw rod.
In the case of a different conventional apparatus for chucking and releasing a conical shank of a tool, for example German OS No. 23 16 605, the draw rod is surrounded by an ejector pipe which is concentric with respect to the draw rod to avoid the abovelisted disadvantages. After separation of the thread connection between the draw rod and tool shank, the ejector pipe is moved in an axial direction through a suitable drive connection and ejects the conical tool shank from the receiving cone. Since, however, the shank is already released from the draw rod, this conventional apparatus is suited only for lighter tools on horizontal drilling and milling systems. Heavier tools must be gripped by an additional tool exchanger. When using this known apparatus on tool machines with a vertical spindle there exists an increased danger of an accident, because the ejected tool may suddenly fall downwardly if a tool-changing apparatus was not moved into position prior to this.
In a further conventional device for chucking and releasing the tool shank on tool machines, for example German OS No. 24 12 850, the draw rod is surrounded by a threaded sleeve which can be screwed into threads in the spindle. The thread pitch of the thread sleeve and the thread pitch of the thread which is provided at the end of the draw rod correspond. Cooperating stops are provided on the thread sleeve and on the draw rod which permit a relative rotation between both parts of slightly less than one rotation. Also, a spring which is initially tensioned in an axial direction is provided between both parts. Upon starting the release operation, the draw rod first rotates by itself but, due to the initially tensioned spring, it cannot move upwardly in an axial direction. Since axial movement of the draw rod is prevented, the conical shank is pressed out of the receiving cone. After slightly less than one rotation, the stops on the thread sleeve and draw rod will rest on one another. Upon further rotation of the draw rod, the thread sleeve is also rotated due to the stops and is moved upwardly in the same degree as the draw rod. The thread of the draw rod can now screw out of the shank. The function of this known apparatus, however, is to a great degree dependent on the friction between the cooperating elements and is thus susceptible to trouble. A further important disadvantage of this known apparatus is its inability to lift heavy additional aggregates, especially angle milling heads, which are connected to the spindle, to couple its spindle carrier with the spindle, and if needed to swing the angle milling head quickly, safely and without any further auxiliary means about the axis of the spindle into a different working position.
The basic purpose of the invention is therefore to produce an apparatus of the abovementioned type for chucking and releasing a conical shank of a tool or an additional aggregate on tool machines, in particular drilling and milling machines, which by avoiding the above disadvantages works substantially wear-free, permits a secure chucking and releasing of the shank and, if desired, also permits rotation of the shanks of heavier additional aggregates, like angle milling heads, without any further auxiliary means.